The new script installation UI is a bit of a change. When I first wrote Greasemonkey, it was intended to be for JavaScript hackers only. I didn't envision there even being a UI at first -- just some configuration files. But now that lots of non-programmers use Greasemonkey, displaying the source code when you click on a user script doesn't make much sense.

When you click on a user script now, it pops up an installation dialog that shows the title, description, and pages the script will be included on. If you want to see the source code, you can still do that by clicking "View Script Source" in the install dialog or in the user script's context menu.